Project Summary/Abstract: Project 4 Thermal treatment of hazardous waste including Superfund Site wastes and soils leads to the formation of environmentally persistent free radicals (EPFRs) associated with emitted particulate matter (PM). Many metals such as copper, iron, zinc or nickel present in PM form EPFRs with varying yields and different degrees of stabilization and persistency. Such EPFR entities were shown to be potentially a primary factor causing the observed cardiopulmonary health effects in exposed populations. Our studies of model systems containing particles with single metal speciation and associated EPFRs has allowed for significant advancement in understanding the formation mechanism of EPFRs as well as the respiratory and cardiac health effects resulting from EPFR exposure. The central hypothesis of Project 4 is that the formation of EPFRs and their biological activation and their propensity to undergo catalytic cycle, producing ?OH, is defined by the constituents of PM and physico-chemical properties of the media (media pH, ionic strength, and polarity) accelerate or prevent EPFR activation. Major scientific questions explored by Project 4 include 1) how does the persistent EPFR in ambient air transform to very active, redox cycling species in biological systems and 2) can the reactivity of EPFRs be exploited as a means to prevent or control EPFR formation and their detection? Project 4 takes a systematic approach to address these questions, starting with defining the mechanism by which EPFRs transition from persistent radicals to reactive species generating OH (i.e., activation). A bottom- up approach is used in the studies; results obtained from laboratory-made samples with simple composition will be compared and evaluated against more complex combustion-generated EPFRs and, finally, field- collected EPFRs. Capitalizing on the results from previous studies, we propose a method for EPFR prevention formation that will be studied in detail. This method is based on the ?in situ? deactivation of the metal centers in thermal treatment (TT) facilities, thus effectively blocking the EPFR emissions. The field sensor development is based on EPFR propensity to generate hydroxyl radicals and is based on the visible light absorption by sensory solution. The results of these studies will provide a basis for technology development to control the emission of EPFRs during TT of Superfund sites materials and to develop devices for simple and fast detection and measurement of EPFRs in field.